Today, much of the Arabian Peninsula is sandy, dry and desolate.
But in recent decades, some scientists have been collecting
evidence revealing past periods of warm, wetter weather that
periodically "greened" swaths of the peninsula, creating
savanna-like environments similar to East Africa's.

The last phase of humid weather is thought to have occurred
between roughly 11,000 and 6,000 years ago before arid conditions
returned and the desert advanced once more. Now, new research on
animal images depicted in rock art from prehistoric humans in
northwest Saudi Arabia is shedding light on the animals and
people that once roamed the region and how they may have been
affected by those changes in climate.

The research reveals that lions, leopards, hyenas and cheetahs
simultaneously thrived in the area during the last period of
wetter weather. That "wealth of carnivores" suggests that copious
amounts of prey and a "mosaic" of different habitats flourished
too, said Maria Guagnin, an archaeologist at
the University of Oxford in England and the study's lead author.

"There is a lot of environmental and biological information
captured in the images," she said. The rock art depicts "the way
the engravers saw their environment and captured [it] for us to
look at millennia later."

Previously, some scientists have suggested that savanna animals
may have moved into the region when the climate was more humid.
But no animal bones have been unearthed to lend support to the
idea. That's in part because preservation of the remains tends to
be poor in the current desert environment and because
archaeological interest in the pre-Islamic period of the region
is somewhat new, and few excavations have taken place.

So the researchers turned to the petroglyphs (carved images, as opposed to
pictographs, which are painted onto rock), which decorate the
sandstone at a place called Shuwaymis, near the northwestern city
of Hail. There, rocky outcrops rise above the harsh landscape on
either side of a dry waterway.

Although Bedouin nomads have likely known of the images, which
are thought to be some of the oldest engravings in Arabia, for
centuries, it wasn't until 2001 that the Saudi government was
alerted to the rock art's existence. In 2015, the site and
another outside the nearby oasis of Jubbah were named Unesco World Heritage sites, bringing global
recognition of the sites' historical value. More than 1,500 rock
art and inscription sites are documented throughout the country,
according to Saudi tourism officials.

In 2013, researchers with the Paleodeserts Project, a collaboration between the
University of Oxford and the Saudi Commission for Tourism and
National Heritage, mapped a portion of the art including 254
panels with images of animals.

In the new study, published in May in
the journal The Holocene, the researchers analyzed the animal
engravings, identifying about 1,500 animals from 16 species. Rock
art is notoriously hard to date, but they were able to divide
most of the images into two broad groups: an early period that
coincided with the wetter environment and a later period from
after the return of the desert. (Their chronology largely matches
the timetable proposed in 2007 by archaeologist Majeed Khan, one of the first
people to study the art.)

They found that the early engraving period contains a wide range
of wild animals including cheetah, leopard, hyena, Arabian wolf,
gazelle, lion, ibex and a type of wild ass known as an onager.
Domesticated animals like hunting dogs and cattle show up, too,
and hint at the transition among humans from hunter-gathers to
herders.

In the later phase, however, the depiction of wild animals
largely ceases. The images of cattle disappear too, suggesting
that the pastures had all dried up. Instead, the art is filled
with desert-adapted domestic animals such as camels, horses and
donkeys.

Still, the researchers were surprised to observe only 16 species
in the art, all of which can survive in relatively arid
conditions. In similar work done by Guagnin in the Sahara Desert,
a wider range of other savanna animals such as hippos and
crocodiles tends to show up in the art when the climate there was
wetter.

But, they argue, for lions, leopards and cheetahs to have lived
in the same environment at the same time, there would have had to
have been substantial amounts of prey such as gazelles and
onagers, and plenty of food for those animals to eat, too. Using
biomass estimates, they conclude that a typical pride of lions
would have required nearly 84,000 pounds of prey or roughly 166
onagers to be present in the area at all times so that the lions
could kill individual onagers without causing the entire
population to decline. A single leopard would have needed roughly
72 mountain gazelles.

What's more, the simultaneous presence of the carnivores implies
a medley of habitats too, from thicker vegetation around
ephemeral waterways, also called wadis, to more open vegetation
in the surrounding landscape. That's because the animals hunt
prey of different sizes and from different habitats, said
Guagnin.

And the carnivores themselves require various environments. For
example, leopards can survive in dry landscapes, she said, "but
if they have competition from lions and cheetah, then they really
need trees where they can hide their prey. Otherwise, the larger
predators would steal it from them. So, we know there must have
been more forested habitat along the wadi courses where the
leopard was able to hunt and live."

The researchers' climate models suggest that during the humid
phase that ended about 6,000 years ago, Shuwaymis was located
near the northern edge of the wet area and, thanks to rain from
the African summer monsoons, may have had ecological corridors
that linked to habitats in the southwest of the peninsula.

"The real beauty of this paper is the way they've interwoven an
understanding of the biology of these animals with climate
modeling and with the actual documentation of the rock art," said
Sandra Olsen, an archaeologist
at the Biodiversity Institute and Natural History Museum at the
University of Kansas, who wasn't involved in the research. "It's
nice to bring all of those pieces of the puzzle together."

For now, Guagnin and her colleagues plan to keep squeezing as
much information as they can out of the stones at Shuwaymis and
other rock art sites in Saudi Arabia, including potential
insights into the artists who left their mark on the rock.

For example, on one of her favorite panels, two hunters seem to
be pursuing a wild ass along with 22 dogs. Rather than a generic
dog figure carved over and over, each dog looks different, with
distinctive ears, tails, chests or stances. "You can really tell
that [the artists] knew each of these dogs. ... You can connect
to the engravers in a way, and that's very nice," she said.